1. Field of the Invention
The present invention relates to an optical transceiver applied in an optical communication.
2. Related Prior Art
The United States Patent application published as US 2002/0149821A has disclosed an optical transceiver with the SFP (Small Form factor Pluggable) configuration, where the transceiver terminates or starts the operation for outputting an optical signal in response to a state, the high level or the low level, of the TX_DISABLE signal sent from the host controller. A multi source agreement provided from the SFF committee has disclosed the specification of the SFP transceiver.
When an optical transceiver is applied in the WDM (Wavelength Division Multiplexing) system, a plurality of optical signals each transmitted from individual optical transceiver is multiplexed by an optical multiplexer to transmit on an optical transmission line. Thus multiplexed signal is amplified by optical amplifiers arranged on the transmission line. The optical amplifier, which includes an optical excitation source, adjusts the power of the excitation source, by monitoring the power of the input and output of the optical signals, so as to keep the optical gain thereof.
Each transceiver in the WDM system outputs the optical signal, which is directly or indirectly modulated by the electrical signal input therein. This state, namely, a state outputting a modulated optical signal, is called as the ON state. On the other hand, the optical transceiver is sometimes compelled to stop the modulation independent of the input electrical signal by a command sent from the host system, or to keep the optical output power constant at a preset level smaller than the low level in the ON state, which is called as the OFF state. The transition from the ON state to the OFF state is often called as the DISABLE of the optical output, while, the transition from the OFF state to the ON state is sometimes called as the ENABLE of the optical output.
In the WDM system, the input level of the optical amplifier depends on the states of the optical transceivers that send optical signals in the optical transmission line. As explained, the optical amplifier operates to keep the optical gain thereof constant; the time constant to keep the optical gain is slower than the time constant to change the state of the optical transceiver, namely, a time from the ON state to the OFF state or from the OFF state to the ON state. Accordingly, the gain of the optical amplifier becomes excessive or insufficient during the transition period of the optical gain, which disarranges the optical level of each optical signal. In the WDM system with a long reach, the optical signal transmitted in the optical transmission line is amplified by a plurality of the optical amplifiers until the signal reaches the end station, which accumulates the variation of the optical levels of each signal.